The disclosure of Japanese Patent Application No. 2000-7959 filed on Jan. 17, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an intake duct for introducing outside air into an air cleaner of an internal combustion engine, for example, a vehicle engine.
2. Discussion of Related Art
An intake duct of this type normally has a hollow cylindrical shape, and the outside air admitted into an air cleaner through the duct generates intake noise such as air-column resonance. In order to reduce such intake noise, an intake duct disclosed in, for example. Japanese Application Laid-Open No. SHO 63-285257 uses an air-permeable porous material to form a part of a circumferential wall of a duct body.
As shown in FIG. 6, in the aforementioned intake duct 51, an intake port 53 for admitting the outside air is formed at one end of a duct body 52. Moreover, a connection port 54 connected to an air cleaner (not shown) through a hose (not shown) or the like is formed at the other end of the duct body 52.
A circumferential wall 55 between the intake port 53 and the connection port 54 of the duct body 52 provides a curved surface over the entire circumference thereof. An opening 56 is formed in the circumferential wall 55, and a porous material 57 is bonded to cover the opening 56. The porous material 57 is formed in a shape matching the shape of the circumferential wall 55 of the duct body 52. For example, a non-woven fabric article to which a desired shape is given by press molding is used as the porous material 57. The non-woven fabric article may be formed from synthetic resin fibers that are pressed without being woven.
By forming a part of the circumferential wall 55 of the duct body 52 from the air-permeable porous material 57, the balance between the amount of outside air admitted through the intake port 53 and the amount of outside air admitted through the porous material 57 can be adjusted. As a result, a natural frequency of the intake duct 51 is varied such that air-columnar resonance in a range of normal use of the vehicle engine is suppressed, and the intake noise is reduced.
Thus, the intake noise can be effectively reduced by using the porous material 57 to form a part of the circumferential wall 55 of the duct body 52. In the above-described conventional structure, however, the porous material 57 forming a part of the circumferential wall 55 of the duct body 52 needs to be formed or shaped in accordance with the shape of the circumferential wall 55 of the duct body 52. Thus, the production of the conventional intake duct 51 requires the step of forming the porous material 57 to match the shape of the circumferential wall 55, using molds having complicated structures for forming the porous material 57 as well as the duct body 52. Moreover, respective molds for the porous material 57 and the duct body 52 need be prepared for each intake duct 51 to be produced. Thus, the intake duct 51 of the conventional structure may suffer from undesirably high manufacturing cost.
Moreover, a gap or clearance between the porous material 57 and the circumferential wall 55 of the duct body 52 may allow the outside air to be admitted into the duct body 52. If such a gap is formed, the amount of outside air admitted through the porous material 57 and the amount of outside air introduced without passing through the porous material 57 is unbalanced, thereby possibly making it difficult to suppress the aircolumnar resonance in the range of normal use of the vehicle engine. Therefore, it is required to accurately bond the porous material 57 to the duct body 52, or to bond the porous material 57 to the duct body 52 via a separate sealing material (not shown), which may result in a significant increase in the manufacturing cost of the intake duct 51.
It is an object of the invention to provide an intake duct in which intake noise can be effectively reduced and which can be produced at a relatively low cost, and to provide a method of producing such an intake duct.
To accomplish the object and other objects, there is provided according to the first aspect of the invention an intake duct adapted to introduce outside air into an air cleaner of an internal combustion engine, which comprises: a hollow duct body including a circumferential wall formed of a resin, with the duct body having an opening formed in a portion of the circumferential wall to provide an end face that lies in a substantially flat plane. A piece of non-woven fabric is joined to the duct body so as to cover the opening. Further, the piece of non-woven fabric is fixed to the duct body by having some of the resin of the duct body penetrate into and solidify with the non-woven fabric.
In the intake duct constructed as described above according to the invention, the opening of the duct body is formed in a flat plane, and the piece of non-woven fabric is simply formed in a flat shape. This eliminates a need to form the piece of non-woven fabric into a curved profile, or the like, corresponding to the shape of the circumferential wall of the duct body. This leads to a greatly simplified structure of a mold for forming the piece of non-woven fabric, and also eliminates a need to prepare a mold for the non-woven fabric for each type of intake duct. Accordingly, the manufacturing cost of the intake duct can be significantly reduced.
The piece of non-woven fabric is joined and fixed to the duct body by having some of the resin of the duct body penetrate into the interior of the article. This arrangement makes it possible to prevent a gap or clearance from being formed between the circumferential wall of the duct body and the non-woven fabric, without requiring accurate formation of the non-woven fabric or providing a sealing material between the duct body and the non-woven fabric. Accordingly, in the intake duct, a suitable balance between the amount of outside air admitted through the non-woven fabric and the amount of outside air admitted without passing through the non-woven fabric is favorably maintained, and intake noise can be effectively reduced during normal operation of the engine. Furthermore, since accurate formation of the non-woven fabric and the sealing material are not needed, the manufacturing cost of the intake duct can be further reduced.